Great to be back. I hope you obsessively played bridge during the grim winter.

From the time we learn the game, we are told, “When defending a NoTrump contract, always lead the fourth best card from your longest suit.” There are exceptions. With East dealing and no one vulnerable, you hold these cards as

South:
♠️ A 5 4
♥️ K Q 7 5 4
♦️ A 6
♣️Q 10 6

The bidding has proceeded as follows:
East            South        West            North
1NT            Pass            3NT            All Pass

What do you lead?

If you play the ♥️5 —fourth best from your longest suit — I guarantee you will lose to both the ♥️J and ♥️A. It usually requires 25 high-card points to bid 3NT, and you have 15. That leaves nothing for partner. Don’t lead the ♥️K because that will needlessly sacrifice a trick. Therefore make a safe lead, say the ♠️4, and  your ♥️K Q may take two tricks if East has the ♥️A.

Here’s another hand:

    ♠️ 10 4
    ♥️ K Q 10 6 4
    ♦️ A 5 4
    ♣️ Q 6 3

Again the bidding proceeds as follows:

East            South        West            North
1NT            Pass            3NT            All Pass

What do you lead?

An exception to the fourth-best lead is to play the top of a sequence or broken sequence.. The ♥️ K Q 10 qualifies, so play the ♥️K. If you lead a low ♥️, you once more will probably lose to the ♥️J and ♥️A.

So the next time you’re on lead against a NoTrump contract, think twice before leading the fourth best in your longest suit.